Determination of free and total available ferulic acid in different types of Chinese Angelica by high performance liquid chromatography

Free and conjugated forms of ferulic acid (FA) are generally available in higher plant taxa such as Chinese Angelica (CA, the roots of Angelica sinensis (Oliv.) Diels). These various forms of FA were found readily inter-convertible and the extractable level of each depended on solvent properties and acidity. Extraction efficiency using various pH solutions namely, water, 70% methanol, methanol-formic acid (95:5) and methanol-2% NaHCO₃ in water (95:5) was compared. Extractable FA were found varying in samples under neutral solvents extraction, whilst relatively consistent for slightly acidic and alkali solvents which were therefore chosen as the optimal media to extract and determine the reproducible levels of free and total available FA. An accurate and rapid high performance liquid chromatographic (HPLC) analysis was conducted using an Alltima C18 column (5 μm, 4.6 mm i.d. × 250 mm) with a guard column (C₁₈, 5 μm, 4.6 mm i.d. × 7.5 mm) at 30°C, eluted with a mixture of 1.0% acetic acid and acetonitrile in a gradient program at a flow rate of 1.0 mL/min and detected at 320 nm. Altogether 20 different types of CA samples including whole root, root head, rootlets, whole root slice, Angelica processed by Chinese yellow wine, and charred Angelica were quantified for free and total available FA. Total available FA was found more abundant than free counterpart with an average ratio of 3.15 (n = 20) in the range of 1.29 to 8.23 for these CA samples. The extraction protocol was proven reliable to quantitatively convert all conjugated FA into its free forms and thereby accurately determined by HPLC method for quality assessment.